Children with asthma are particularly vulnerable to environmental tobacco smoke (ETS). However, despite this special vulnerability to ETS, children with asthma are at least as likely to live in smoking households, as are healthy children. Controversy exists, however, about whether or not the smoking members of households with children with asthma use specific strategies to reduce the harmful effects of their smoking on their children more than the smoking members of households of healthy children. The central aim of this case-control study is to examine whether or not primary school-aged children with asthma from low-income households have lower household ETS exposure than matched control children. Household ETS exposure will be measured by both objective monitoring, specifically passive nicotine dosimeters and child cotinine assays (the primary hypothesis), and maternal-report (the secondary hypothesis). Ninety children with physician diagnosed asthma and smoking mothers will be matched by age, gender, race/ethnicity, and other relevant variables to 90 healthy children. All children will be recruited from Metro Denver clinics providing services to low-income, underserved populations. The sample will contain equal numbers of African Americans, Hispanics, and Whites. Recruitment will target low-income populations due to their increased prevalence of, and associated morbidity from both asthma and tobacco smoking. We will also examine how specific household smoking behaviors, as reported by mothers, are associated with household nicotine and child cotinine levels. Finally, we have included a set of carefully chosen measures that will be examined in tertiary, exploratory analyses to help understand, clarify, and contextualize the observed results. This study has been carefully designed to correct the serious methodological problems of the prior work in this area. Accordingly, the proposed study will be able to resolve a number of extremely important child health questions of major theoretical and practical importance: (1) do children with asthma have less household ETS exposure as measured by objective monitoring than healthy children; (2) do alterations in household smoking behavior account for this difference; and if so, (3) which specific strategies are effective in reducing children's ETS exposure and which are not? Knowing the answers to these questions, as well as whether there is significant racial/ethnic variability in the answers, will be invaluable to ongoing tobacco intervention and control efforts in families of children with asthma, as well as other vulnerable populations.